Known variable valve timing control devices ensure appropriate operational state of an engine by varying relative rotational phases of a driving side rotational member such as an external rotor rotating synchronized with a crankshaft and a driven side rotational member such as an inner rotor connected with a camshaft at a normal operation of the engine.
The known variable valve timing control devices include a rotational phase holding mechanism (i.e., a lock mechanism) for holding and allowing the relative rotation between the driving side rotational member and the driven side rotational member. The lock mechanism maintains a lock release state when changing the relative rotational phase. A locked state is, for example, achieved at timing for ensuring a predetermined relative rotational phase such as at an engine start.
In other words, the lock mechanism assumes a locked position at the engine start and assumes a lock release position at a normal operation. Thus, the appropriate starting state is ensured at the engine start.
The lock mechanism includes a lock body moving from the first rotational member side to enter the second rotational member side (i.e., of either the driving side rotational member or the driven side rotational member). By the lock body extended both in the first and the second rotational members, the locked position for holding the relative rotation is achieved. In the meantime, by the retraction of the lock body to the first rotational member side, the relative rotation between the first rotational member and the second rotational member is allowed to assume the lock release position.
A known variable valve timing control device includes a rotational phase restriction mechanism for restricting the relative rotation between the driving side rotational member and the driven side rotational member separating from a locked phase and for allowing the relative rotation between the driving side rotational member and the driven side rotational member approximating to the locked phase by the construction between a restriction body (i.e., corresponding to the lock body of the lock mechanism) and a groove width of a groove formed at the rotational member for receiving the restriction body to be extended in the peripheral direction.
The rotational phase restriction mechanism restricts the relative rotation to a retarded angle side and allows the relative rotation to an advanced angle side at a restriction phase determined, for example, between a most retarded angle phase and the locked phase in case the locked phase is determined at an intermediate phase region between the most retarded angle phase and a most advanced angle phase. With the restriction by the rotational phase restriction mechanism, the relative rotation between the driving side rotational member and the driven side rotational member does not move to the retarded angle side equal to or further than the restriction phase.
A known variable valve timing control device described in Japanese Patent Laid-Open Publication No. 2002-97912 includes the rotational phase restriction mechanism. With the rotational phase restriction mechanism of the variable valve timing control device described in Japanese Patent Laid-Open Publication No. 2002-97912, an engine start lock operation for locking by changing the relative rotational phase from the most retarded angle phase to the locked phase at the engine start is performed swiftly.
With the construction of the variable valve timing control device described in Japanese Patent Laid-Open Publication No. 2002-97912, the rotational phase change from the most retarded angle phase to the locked phase corresponding to the intermediate advanced angle is carried out with steps by one-fourth phase of the phase differences between the most retarded angle phase and the locked phase by providing an auxiliary restriction mechanism serving as the rotational phase restriction mechanism.
The variable valve timing control device described in Japanese Patent Laid-Open Publication No. 2002-97912 includes a rotational phase holding mechanism including a first control mechanism and a second control mechanism. The rotational phase holding mechanism further includes the single auxiliary restriction mechanism. A lock groove includes a step serving as the auxiliary restriction mechanism.
With the variable valve timing control device described in Japanese Patent Laid-Open Publication No. 2002-97912, the reaching time to the locked phase is shortened by raising the level of an initial value of the relative rotation by a predetermined value by providing the mechanism for restricting the relative rotation to the retarded angle direction during the relative rotation from the phase before the engine start (e.g., the most retarded angle) to the locked phase serving as the intermediate phase by the fluctuation torque applied to a camshaft (shown in FIG. 13).
Notwithstanding, with the construction of the known variable valve timing control device described in Japanese Patent Laid-Open Publication No. 2002-97912, the reaching time to the locked phase assumes long at the low temperature environment due to the increase of the resistance when draining the remained oil in a fluid chamber used for adjusting the relative rotational phase to reduce the relative rotational width due to the fluctuation torque of the camshaft.
A need thus exists for a variable valve timing control device which achieves a swift and secure engine start lock with a simple construction.